Liquid-crystal medium

ABSTRACT

The invention relates to a liquid-crystalline medium, in particular based on a mixture of polar compounds, and to the use thereof for an active-matrix display, in particular based on the VA, SA-VA, IPS, PS-IPS, FFS, PS-FFS, UB-FFS or PS-UB-FFS effect.

SUMMARY OF THE INVENTION

The invention relates to a liquid-crystalline medium, in particularbased on a mixture of polar compounds, and to the use thereof for anactive-matrix display, in particular based on the VA, SA-VA, IPS,PS-IPS, FFS, PS-FFS, UB-FFS or PS-UB-FFS effect.

Media of this type can be used, in particular, for electro-opticaldisplays having active-matrix addressing based on the ECB effect and forIPS (in-plane switching) displays or FFS (fringe field switching)displays.

The principle of electrically controlled birefringence, the ECB effector also DAP (deformation of aligned phases) effect, was described forthe first time in 1971 (M. F. Schieckel and K. Fahrenschon, “Deformationof nematic liquid crystals with vertical orientation in electricalfields”, Appl. Phys. Lett. 19 (1971), 3912). This was followed by papersby J. F. Kahn (Appl. Phys. Lett. 20 (1972), 1193) and G. Labrunie and J.Robert (J. Appl. Phys. 44 (1973), 4869).

The papers by J. Robert and F. Clerc (SID 80 Digest Techn. Papers(1980), 30), J. Duchene (Displays 7 (1986), 3) and H. Schad (SID 82Digest Techn. Papers (1982), 244) showed that liquid-crystalline phasesmust have high values for the ratio of the elastic constants K₃/K₁, highvalues for the optical anisotropy Δn and values for the dielectricanisotropy of Δε≤−0.5 in order to be suitable for use inhigh-information display elements based on the ECB effect.Electro-optical display elements based on the ECB effect have ahomeotropic edge alignment (VA technology=vertically aligned).Dielectrically negative liquid-crystal media can also be used indisplays which use the so-called IPS or FFS effect.

Displays which use the ECB effect, as so-called VAN (vertically alignednematic) displays, for example in the MVA (multi-domain verticalalignment, for example: Yoshide, H. et al., paper 3.1: “MVA LCD forNotebook or Mobile PCs . . . ”, SID 2004 International Symposium, Digestof Technical Papers, XXXV, Book I, pp. 6 to 9, and Liu, C. T. et al.,paper 15.1: “A 46-inch TFT-LCD HDTV Technology . . . ”, SID 2004International Symposium, Digest of Technical Papers, XXXV, Book II, pp.750 to 753), PVA (patterned vertical alignment, for example: Kim, SangSoo, paper 15.4: “Super PVA Sets New State-of-the-Art for LCD-TV”, SID2004 International Symposium, Digest of Technical Papers, XXXV, Book II,pp. 760 to 763), ASV (advanced super view, for example: Shigeta,Mitzuhiro and Fukuoka, Hirofumi, paper 15.2: “Development of HighQuality LCDTV”, SID 2004 International Symposium, Digest of TechnicalPapers, XXXV, Book II, pp. 754 to 757) modes, have establishedthemselves as one of the three more recent types of liquid-crystaldisplay that are currently the most important, in particular fortelevision applications, besides IPS (in-plane switching) displays (forexample: Yeo, S. D., paper 15.3: “An LC Display for the TV Application”,SID 2004 International Symposium, Digest of Technical Papers, XXXV, BookII, pp. 758 & 759) and the long-known TN (twisted nematic) displays. Thetechnologies are compared in general form, for example, in Souk, Jun,SID Seminar 2004, seminar M-6: “Recent Advances in LCD Technology”,Seminar Lecture Notes, M-6/1 to M-6/26, and Miller, Ian, SID Seminar2004, seminar M-7: “LCD-Television”, Seminar Lecture Notes, M-7/1 toM-7/32. Although the response times of modern ECB displays have alreadybeen significantly improved by addressing methods with overdrive, forexample: Kim, Hyeon Kyeong et al., paper 9.1: “A 57-in. Wide UXGATFT-LCD for HDTV Application”, SID 2004 International Symposium, Digestof Technical Papers, XXXV, Book I, pp. 106 to 109, the achievement ofvideo-compatible response times, in particular on switching of greyshades, is still a problem which has not yet been satisfactorily solved.

Industrial application of this effect in electro-optical displayelements requires LC phases, which have to satisfy a multiplicity ofrequirements. Particularly important here are chemical resistance tomoisture, air and physical influences, such as heat, infrared, visibleand ultraviolet radiation and direct and alternating electric fields.

Furthermore, industrially usable LC phases are required to have aliquid-crystalline mesophase in a suitable temperature range and lowviscosity.

None of the hitherto-disclosed series of compounds having aliquid-crystalline mesophase includes a single compound which meets allthese requirements. Mixtures of two to 25, preferably three to 18,compounds are therefore generally prepared in order to obtain substanceswhich can be used as LC phases. However, it has not been possible toprepare optimum phases easily in this way since no liquid-crystalmaterials having significantly negative dielectric anisotropy andadequate long-term stability were hitherto available.

Matrix liquid-crystal displays (MLC displays) are known. Non-linearelements which can be used for individual switching of the individualpixels are, for example, active elements (i.e. transistors). The term“active matrix” is then used, where a distinction can be made betweentwo types:

-   1. MOS (metal oxide semiconductor) transistors on a silicon wafer as    substrate-   2. thin-film transistors (TFTs) on a glass plate as substrate.

In the case of type 1, the electro-optical effect used is usuallydynamic scattering or the guest-host effect. The use of single-crystalsilicon as substrate material restricts the display size, since evenmodular assembly of various part-displays results in problems at thejoints.

In the case of the more promising type 2, which is preferred, theelectro-optical effect used is usually the TN effect.

A distinction is made between two technologies: TFTs comprising compoundsemiconductors, such as, for example, CdSe, or TFTs based onpolycrystalline or amorphous silicon. The latter technology is beingworked on intensively worldwide.

The TFT matrix is applied to the inside of one glass plate of thedisplay, while the other glass plate carries the transparentcounterelectrode on its inside. Compared with the size of the pixelelectrode, the TFT is very small and has virtually no adverse effect onthe image. This technology can also be extended to fully color-capabledisplays, in which a mosaic of red, green and blue filters is arrangedin such a way that a filter element is opposite each switchable pixel.

The term MLC displays here covers any matrix display with integratednon-linear elements, i.e. besides the active matrix, also displays withpassive elements, such as varistors or diodes(MIM=metal-insulator-metal).

MLC displays of this type are particularly suitable for TV applications(for example pocket TVs) or for high-information displays in automobileor aircraft construction. Besides problems regarding the angledependence of the contrast and the response times, difficulties alsoarise in MLC displays due to insufficiently high specific resistance ofthe liquid-crystal mixtures [TOGASHI, S., SEKIGUCHI, K., TANABE, H.,YAMAMOTO, E., SORIMACHI, K., TAJIMA, E., WATANABE, H., SHIMIZU, H.,Proc. Eurodisplay 84, September 1984: A 210-288 Matrix LCD Controlled byDouble Stage Diode Rings, pp. 141 ff., Paris; STROMER, M., Proc.Eurodisplay 84, September 1984: Design of Thin Film Transistors forMatrix Addressing of Television Liquid Crystal Displays, pp. 145 ff.,Paris]. With decreasing resistance, the contrast of an MLC displaydeteriorates. Since the specific resistance of the liquid-crystalmixture generally drops over the life of an MLC display owing tointeraction with the inside surfaces of the display, a high (initial)resistance is very important for displays that have to have acceptableresistance values over a long operating period.

There thus continues to be a great demand for MLC displays having veryhigh specific resistance at the same time as a large working-temperaturerange, short response times and a low threshold voltage with the aid ofwhich various grey shades can be produced.

The disadvantage of the frequently-used MLC-TN displays is due to theircomparatively low contrast, the relatively high viewing-angle dependenceand the difficulty of generating grey shades in these displays.

VA displays have significantly better viewing-angle dependencies and aretherefore principally used for televisions and monitors. However, therecontinues to be a need here to improve the response times, in particularwith respect to the use of televisions having frame rates (image changefrequency/repetition rates) of greater than 60 Hz. At the same time,however, the properties, such as, for example, the low-temperaturestability, must not be impaired.

Another problem which could be observed in TFT displays like those ofthe UB-FFS mode is the appearance of flicker, which is a time dependentvariation in brightness, i.e. the brightness fluctuates during thecharging and holding periods in display operation. The main reasonscausing flicker include generation of residual DC charge for example dueto impurities, an asymmetric voltage between the electrodes or aflexoelectric effect. The flicker induced by the flexoelectric effectcan be evaluated by the so-called white flicker method as described inthe example section.

Another problem is the occurrence of image sticking (or image burn),wherein the image produced in the LC display by temporary addressing ofindividual pixels still remains visible even after the electric field inthese pixels has been switched off or after other pixels have beenaddressed. This can be evaluated by measuring the easy axis shift, whichindicates the difference between the initial off-state orientationdirection of the LC molecules relative to the substrate and theiroff-state orientation after several addressing cycles.

The invention provides liquid-crystal mixtures, in particular formonitor and TV applications, which are based on the ECB effect or on theIPS or FFS effect, which do not have the above-mentioned disadvantagesor only do so to a reduced extent. In particular, it must be formonitors and televisions the mixtures allow the displays to operate atextremely high and extremely low temperatures and at the same time tohave short response times and improved reliability behavior, inparticular no or significantly reduced image sticking after longoperating times.

The LC medium as described and claimed hereinafter provides thesefeatures.

The use of an LC mixture as disclosed and claimed hereinafter havingnegative dielectric anisotropy surprisingly results in very lowrotational viscosities and in a reduction in the ratio of rotationalviscosity and elastic constants, while maintaining a high reliabilityand high VHR values also after UV exposure. Liquid-crystal mixtures,preferably VA, PS (=polymer stabilised)-VA, SA (=self alignment)-VA,IPS, PS-IPS, PS-FFS, FFS mixtures, in particular UB-FFS (ultrabrightness fringe field switching) or PS-UB-FFS mixtures, which haveshort response times and good reliability, and at the same time goodphase properties and good low-temperature behavior can therefore beprepared.

The invention relates to a liquid crystal (LC) medium having negativedielectric anisotropy and comprising one or more compounds of formula LB

in which the individual radicals, on each occurrence identically ordifferently, and each, independently of one another, have the followingmeaning:

-   R¹ alkyl, alkoxy, oxaalkyl or alkoxyalkyl having 1 to 9, preferably    1 to 6, C atoms or alkenyl or alkenyloxy having 2 to 9, preferably 2    to 6, C atoms, all of which are optionally fluorinated,-   L¹, L² F or Cl, preferably F,-   X¹ fluorinated alkyl or alkoxy with 1, 2 or 3 C atoms, preferably    CF₃ or OCF₃,-   Y¹ O or S.

The invention further relates to the use of an LC medium as describedabove and below used for electro-optical purposes, in particular for theuse in shutter glasses, for 3D applications, or in VA, PS-VA, SA-VA,IPS, PS-IPS, FFS, PS-FFS, UB-FFS or PS-UB-FFS displays.

The invention further relates to an electro-optical LC displaycontaining an LC medium as described above and below, in particular anVA, PS-VA, SA-VA, IPS, PS-IPS, FFS, PS-FFS, UB-FFS or PS-UB-FFS display.

The invention furthermore relates to a process for preparing an LCmedium as described above and below, comprising the steps of mixing oneor more compounds of formula LB with one or more further LC compoundsand optionally one or more additives.

The LC media according to the invention preferably exhibit very broadnematic phase ranges having clearing points≥70° C., preferably ≥75° C.,in particular ≥80° C., very favorable values for the capacitivethreshold, relatively high values for the holding ratio and at the sametime very good low-temperature stabilities at −20° C. and −30° C., aswell as very low rotational viscosities and short response times.

The LC media according to the invention are furthermore distinguished bythe fact that, in addition to the improvement in the rotationalviscosity γ₁, high reliability and high VHR values, even after UVexposure, can be achieved.

The LC media according to the invention are furthermore distinguished bythe fact that, in addition to the improvement in the rotationalviscosity γ₁, relatively high values of the elastic constant K₃ forimproving the response times can be observed. In particular, themixtures according to the invention have a particularly low value forthe ratio γ₁/K₃ of rotational viscosity γ₁ and elastic constant K₃,which is an indicator of a fast response time.

Preferred compounds of formula LB are selected from the followingsubformulae:

wherein R¹ has one of the meanings given in formula LB and preferablydenotes straight-chain alkyl having 1-6 C atoms, very preferably methyl,ethyl, propyl, butyl, pentyl or hexyl, more preferably ethyl or propyl,most preferably propyl.

Very preferred compounds of formula LB are selected from the followingsubformulae:

wherein R¹ has one of the meanings given in formula LB and preferablydenotes straight-chain alkyl having 1-6 C atoms, very preferably methyl,ethyl, propyl, butyl, pentyl or hexyl, more preferably ethyl or propyl,most preferably propyl.

Most preferred are compounds of formulae LB-1-1 and LB2-2.

The total proportion of the compounds of formula LB, LB1, LB2 and theirsubformulae in the LC medium is from >0 to ≤5%, preferably from 0.05 to4%, very preferably from 0.1 to 3%, more preferably from 0.1 to 2%, mostpreferably from 0.5 to 1%, by weight.

Preferably the LC medium contains 1, 2 or 3 compounds of formula LB,LB1, LB2 or their subformulae.

In another preferred embodiment of the present invention the LC mediumcomprises one or more compounds of formula LB1 or its subformulae andone or more compounds of formula LB2 or its subformulae.

In the LC medium according to the present invention one or more of thefollowing advantages could be achieved:

-   -   high transmittance,    -   high contrast ratio,    -   reduced image sticking,    -   reduced ODF mura,    -   high reliability and high VHR value after UV exposure and/or        heat treatment,    -   high birefringence,    -   reduced rotational viscosity    -   faster response times,    -   reduced white flicker,    -   lower easy axis shift ΔΦ.

In a preferred embodiment of the present invention the LC mediumcomprises one or more comprising an alkenyl group, preferably selectedfrom formula AN and AY:

in which the individual radicals, on each occurrence identically ordifferently, and each, independently of one another, have the followingmeaning:

-   R^(A1) alkenyl having 2 to 9 C atoms or, if at least one of the    rings X, Y and Z denotes cyclohexenyl, also one of the meanings of    R^(A2),-   R^(A2) alkyl having 1 to 12 C atoms, in which, in addition, one or    two non-adjacent CH₂ groups may be replaced by —O—, —CH═CH—, —CO—,    —OCO— or —COO— in such a way that O atoms are not linked directly to    one another,-   Z^(x) —CH₂CH₂—, —CH═CH—, —CF₂O—, —OCF₂—, —CH₂O—, —OCH₂—, —CO—O—,    —O—CO—, —C₂F₄—, —CF═CF—, —CH═CH—CH₂O—, or a single bond, preferably    a single bond,-   L¹⁻⁴ H, F, Cl, OCF₃, CF₃, CH₃, CH₂F or CHF₂H, preferably H, F or Cl,-   x 1 or 2,-   z 0 or 1.

Preferred compounds of formula AN and AY are those wherein R^(A2) isselected from ethenyl, propenyl, butenyl, pentenyl, hexenyl andheptenyl.

Further preferred compounds of formula AN and AY are those wherein L¹and L² denote F, or one of L¹ and L² denotes F and the other denotes Cl,and L³ and L⁴ denote F, or one of L³ and L⁴ denotes F and the otherdenotes Cl.

The compounds of the formula AN are preferably selected from thefollowing sub-formulae:

in which alkyl and alkyl* each, independently of one another, denote astraight-chain alkyl radical having 1-6 C atoms, and alkenyl andalkenyl* each, independently of one another, denote a straight-chainalkenyl radical having 2-7 C atoms. Alkenyl and alkenyl* preferablydenote CH₂═CH—, CH₂═CHCH₂CH₂—, CH₃—CH═CH—, CH₃—CH₂—CH═CH—,CH₃—(CH₂)₂—CH═CH—, CH₃—(CH₂)₃—CH═CH— or CH₃—CH═CH—(CH₂)₂—.

Very preferred compounds of the formula AN are selected from thefollowing sub-formulae:

in which m denotes 1, 2, 3, 4, 5 or 6, i denotes 0, 1, 2 or 3, andR^(b1) denotes H, CH₃ or C₂H.

Very particularly preferred compounds of the formula AN are selectedfrom the following sub-formulae:

Most preferred are compounds of formula AN1a2, AN1a5, AN6a1 and AN6a2.

In a preferred embodiment the LC medium contains one or more compoundsselected from formula AN1a2, AN1a5 and AN1a6.

Preferably the LC medium or LC host mixture contains 1 to 5, preferably1, 2 or 3 compounds selected of formula AN or its subformulae.

The proportion of the compounds of formula AN in the LC medium ispreferably from 5 to 70%, more preferably from 10 to 60%, mostpreferably from 20 to 60%.

The compounds of the formula AY are preferably selected from thefollowing sub-formulae:

in which alkyl and alkyl* each, independently of one another, denote astraight-chain alkyl radical having 1-6 C atoms, and alkenyl andalkenyl* each, independently of one another, denote a straight-chainalkenyl radical having 2-7 C atoms. Alkenyl and alkenyl* preferablydenote CH₂═CH—, CH₂═CHCH₂CH₂—, CH₃—CH═CH—, CH₃—CH₂—CH═CH—,CH₃—(CH₂)₂—CH═CH—, CH₃—(CH₂)₃—CH═CH— or CH₃—CH═CH—(CH₂)₂—.

Very preferred compounds of the formula AY are selected from thefollowing sub-formulae:

in which m and n each, independently of one another, denote 1, 2, 3, 4,5 or 6, and alkenyl denotes CH₂═CH—, CH₂═CHCH₂CH₂—, CH₃—CH═CH—,CH₃—CH₂—CH═CH—, CH₃—(CH₂)₂—CH═CH—, CH₃—(CH₂)₃—CH═CH— orCH₃—CH═CH—(CH₂)₂—.

The proportion of compounds of formula AY in the LC medium is preferablyfrom 2 to 50% by weight, very preferably from 5 to 40% by weight, mostpreferably from 5 to 30% by weight.

Preferably the LC medium or LC host mixture contains 1 to 5, preferably1, 2 or 3 compounds selected of formula AY or its subformulae.

In a preferred embodiment of the present invention the LC mediumcomprises one or more compounds of formula AY14, very preferably ofAY14a. The proportion of compounds of formula AY14 or AY14a in the LCmedium is preferably from 3 to 30% by weight.

The addition of alkenyl compounds of formula AN and/or AY enables areduction of the viscosity and response time of the LC medium.

The LC medium preferably comprises no compounds containing a terminalvinyloxy group (—O—CH═CH₂), in particular no compounds of the formula ANor AY in which R^(A1) or R^(A2) denotes or contains a terminal vinyloxygroup (—O—CH═CH₂).

Further preferred embodiments of the LC medium according to the presentinvention are those of sections a)-z) below, including any combinationthereof:

-   a) The LC medium comprises one or more compounds of the formulae CY    and/or PY:

-   -   wherein    -   a denotes 1 or 2,    -   b denotes 0 or 1,

-   -   R¹ and R² each, independently of one another, denote alkyl        having 1 to 12 C atoms, where, in addition, one or two        non-adjacent CH₂ groups may be replaced by —O—, —CH═CH—, —CO—,        —OCO— or —COO— in such a way that O atoms are not linked        directly to one another, preferably alkyl or alkoxy having 1 to        6 C atoms,    -   Z^(x) and Z^(y) each, independently of one another, denote        —CH₂CH₂—, —CH═CH—, —CF₂O—, —OCF₂—, —CH₂O—, —OCH₂—, —CO—O—,        —O—CO—, —C₂F₄—, —CF═CF—, —CH═CH—CH₂O— or a single bond,        preferably a single bond,    -   L¹⁻⁴ each, independently of one another, denote F, Cl, OCF₃,        CF₃, CH₃, CH₂F, CHF₂.    -   Preferably, both L¹ and L² denote F or one of L¹ and L² denotes        F and the other denotes Cl, or both L³ and L⁴ denote F or one of        L³ and L⁴ denotes F and the other denotes Cl.    -   The compounds of the formula CY are preferably selected from the        group consisting of the following sub-formulae:

-   -   in which a denotes 1 or 2, alkyl and alkyl* each, independently        of one another, denote a straight-chain alkyl radical having 1-6        C atoms, and (O) denotes an oxygen atom or a single bond.    -   The compounds of the formula PY are preferably selected from the        group consisting of the following sub-formulae:

-   -   in which alkyl and alkyl* each, independently of one another,        denote a straight-chain alkyl radical having 1-6 C atoms,        and (O) denotes an oxygen atom or a single bond.

-   b) The LC medium comprises one or more compounds of the following    formula:

-   -   in which the individual radicals have the following meanings:

-   -   R³ and R⁴ each, independently of one another, denote alkyl        having 1 to 12 C atoms, in which, in addition, one or two        non-adjacent CH₂ groups may be replaced by —O—, —CH═CH—, —CO—,        —O—CO— or —CO—O— in such a way that O atoms are not linked        directly to one another,    -   Z^(y) denotes —CH₂CH₂—, —CH═CH—, —CF₂O—, —OCF₂—, —CH₂O—, —OCH₂—,        —CO—O—, —O—CO—, —C₂F₄—, —CF═CF—, —CH═CH—CH₂O— or a single bond,        preferably a single bond.    -   The compounds of the formula ZK are preferably selected from the        group consisting of the following sub-formulae:

-   -   in which alkyl and alkyl* each, independently of one another,        denote a straight-chain alkyl radical having 1-6 C atoms.    -   Especially preferred are compounds of formula ZK1.    -   Particularly preferred compounds of formula ZK are selected from        the following sub-formulae:

-   -   wherein the propyl, butyl and pentyl groups are straight-chain        groups.    -   Most preferred are compounds of formula ZK1a.

-   c) The LC medium comprises one or more compounds of the following    formula:

-   -   in which the individual radicals on each occurrence, identically        or differently, have the following meanings:    -   R⁵ and R⁶ each, independently of one another, denote alkyl        having 1 to 12 C atoms, where, in addition, one or two        non-adjacent CH₂ groups may be replaced by —O—, —CH═CH—, —CO—,        —OCO— or —COO— in such a way that O atoms are not linked        directly to one another, preferably alkyl or alkoxy having 1 to        6 C atoms,

-   -   e denotes 1 or 2.    -   The compounds of the formula DK are preferably selected from the        group consisting of the following sub-formulae:

-   -   in which alkyl and alkyl* each, independently of one another,        denote a straight-chain alkyl radical having 1-6 C atoms.

-   d) The LC medium comprises one or more compounds of the following    formula DY:

-   -   in which the individual radicals have the following meanings:

-   -   with at least one ring F being different from cyclohexylene,    -   f denotes 1 or 2,    -   R¹ and R² each, independently of one another, denote alkyl        having 1 to 12 C atoms, where, in addition, one or two        non-adjacent CH₂ groups may be replaced by —O—, —CH═CH—, —CO—,        —OCO— or —COO— in such a way that O atoms are not linked        directly to one another,    -   Z^(x) denotes —CH₂CH₂—, —CH═CH—, —CF₂O—, —OCF₂—, —CH₂O—, —OCH₂—,        —CO—O—, —O—CO—, —C₂F₄—, —CF═CF—, —CH═CH—CH₂O— or a single bond,        preferably a single bond.    -   L¹ and L² each, independently of one another, denote F, Cl,        OCF₃, CF₃, CH₃, CH₂F, CHF₂.    -   Preferably, both radicals L¹ and L² denote F or one of the        radicals L¹ and L² denotes F and the other denotes Cl.    -   The compounds of the formula DY are preferably selected from the        group consisting of the following sub-formulae:

-   -   in which R¹ has the meaning indicated above, alkyl denotes a        straight-chain alkyl radical having 1-6 C atoms, (O) denotes an        oxygen atom or a single bond, and v denotes an integer from 1        to 6. R¹ preferably denotes straight-chain alkyl having 1 to 6 C        atoms or straight-chain alkenyl having 2 to 6 C atoms, in        particular CH₃, C₂H₅, n-C₃H₇, n-C₄H₉, n-C₅H₁₁, CH₂═CH—,        CH₂═CHCH₂CH₂—, CH₃—CH═CH—, CH₃—CH₂—CH═CH—, CH₃—(CH₂)₂—CH═CH—,        CH₃—(CH₂)₃—CH═CH— or CH₃—CH═CH—(CH₂)₂—.

-   e) The LC medium comprises one or more compounds of the following    formula:

-   -   in which the individual radicals, on each occurrence identically        or differently, and each, independently of one another, have the        following meaning:    -   R¹, R² alkyl, alkoxy, oxaalkyl or alkoxyalkyl having 1 to 9 C        atoms or alkenyl or alkenyloxy having 2 to 9 C atoms, all of        which are optionally fluorinated,    -   L^(T1)-L^(T6) H, F or Cl, with at least one of L^(T1) to L^(T6)        being F or Cl,    -   The compounds of the formula T are preferably selected from the        group consisting of the following sub-formulae:

-   -   in which R denotes a straight-chain alkyl or alkoxy radical        having 1-7 C atoms, R* denotes a straight-chain alkenyl radical        having 2-7 C atoms, (O) denotes an oxygen atom or a single bond,        and m denotes an integer from 1 to 6. R* preferably denotes        CH₂═CH—, CH₂═CHCH₂CH₂—, CH₃—CH═CH—, CH₃—CH₂—CH═CH—,        CH₃—(CH₂)₂—CH═CH—, CH₃—(CH₂)₃—CH═CH— or CH₃—CH═CH—(CH₂)₂—.    -   R and R* preferably denote methyl, ethyl, propyl, butyl, pentyl,        hexyl, methoxy, ethoxy, propoxy, butoxy or pentoxy.    -   Very preferred are compounds of formulae T1, T2 and T3,        especially those of formula T1 and T2.    -   Very preferred are compounds of formula T1-T24 wherein (O)        denotes an oxygen atom, m is 1, 2, 3, 4 or 5 and R is methyl,        ethyl, propyl, butyl of pentyl or hexyl, which are preferably        straight-chained.    -   Preferably, the LC medium does not contain more than 15% of        compounds of formula T or T1-T24 or any other compounds with a        terphenyl group.    -   Preferably the proportion of compounds of formula T or T1-T24 or        any other compounds with a terphenyl group in the LC medium is        at least 5%, very preferably from 5 to 15%, most preferably from        5 to 10%.    -   Preferably the LC medium contains 1 to 5, very preferably 1 or 2        compounds of formula T or T1-T24.

-   f) The LC medium comprises one or more compounds selected from the    group consisting of the following formulae:

-   -   in which alkyl denotes C₁₋₆-alkyl, L^(x) denotes H or F, and X        denotes F, Cl, OCF₃, OCHF₂ or OCH═CF₂. Particular preference is        given to compounds of the formula G1 in which X denotes F.

-   g) The LC medium comprises one or more compounds selected from the    group consisting of the following formulae:

-   -   in which R⁵ has one of the meanings indicated above for R¹,        alkyl denotes C₁₋₆-alkyl, d denotes 0 or 1, and z and m each,        independently of one another, denote an integer from 1 to 6. R⁵        in these compounds is particularly preferably C₁₋₆-alkyl or        -alkoxy or C₂₋₆-alkenyl, d is preferably 1. The LC medium        according to the invention preferably comprises one or more        compounds of the above-mentioned formulae in amounts of ≥5% by        weight.

-   h) The LC medium comprises one or more biphenyl compounds selected    from the group consisting of the following formulae:

-   -   in which alkyl and alkyl* each, independently of one another,        denote a straight-chain alkyl radical having 1-6 C atoms, and        alkenyl and alkenyl* each, independently of one another, denote        a straight-chain alkenyl radical having 2-6 C atoms. Alkenyl and        alkenyl* preferably denote CH₂═CH—, CH₂═CHCH₂CH₂—, CH₃—CH═CH—,        CH₃—CH₂—CH═CH—, CH₃—(CH₂)₂—CH═CH—, CH₃—(CH₂)₃—CH═CH— or        CH₃—CH═CH—(CH₂)₂—.    -   The proportion of the biphenyls of the formulae B1 to B3 in the        LC mixture is preferably at least 3% by weight, in particular        ≥5% by weight.    -   The compounds of the formula B2 are particularly preferred.    -   The compounds of the formulae B1 to B3 are preferably selected        from the group consisting of the following sub-formulae:

-   -   in which alkyl* denotes an alkyl radical having 1-6 C atoms. The        medium according to the invention particularly preferably        comprises one or more compounds of the formulae B1a and/or B2c.

-   i) The LC medium comprises one or more compounds selected from the    group consisting of the following formulae:

-   -   in which R¹ and R² have the meanings indicated above and        preferably each, independently of one another, denote        straight-chain alkyl having 1 to 6 C atoms or straight-chain        alkenyl having 2 to 6 C atoms.    -   Preferred media comprise one or more compounds selected from the        formulae 01, 03 and 04.

-   k) The LC medium comprises one or more compounds of the following    formula:

-   -   in which

-   -   R⁹ denotes H, CH₃, C₂H₅ or n-C₃H₇, (F) denotes an optional        fluorine substituent, and q denotes 1, 2 or 3, and R⁷ has one of        the meanings indicated for R¹, preferably in amounts of >3% by        weight, in particular ≥5% by weight and very particularly        preferably 5-30% by weight.    -   Particularly preferred compounds of the formula FI are selected        from the group consisting of the following sub-formulae:

-   -   in which R⁷ preferably denotes straight-chain alkyl, and R⁹        denotes CH₃, C₂H₅ or n-C₃H₇. Particular preference is given to        the compounds of the formulae F₁₁, F₁₂ and F₁₃.

-   l) The LC medium comprises one or more compounds selected from the    group consisting of the following formulae:

-   -   in which R⁸ has the meaning indicated for R¹, and alkyl denotes        a straight-chain alkyl radical having 1-6 C atoms.

-   m) The LC medium comprises one or more compounds which contain a    tetrahydronaphthyl or naphthyl unit, such as, for example, the    compounds selected from the group consisting of the following    formulae:

-   -   in which    -   R¹⁰ and R¹¹ each, independently of one another, denote alkyl        having 1 to 12 C atoms, where, in addition, one or two        non-adjacent CH₂ groups may be replaced by —O—, —CH═CH—, —CO—,        —OCO— or —COO— in such a way that O atoms are not linked        directly to one another, preferably alkyl or alkoxy having 1 to        6 C atoms,    -   and R¹⁰ and R¹¹ preferably denote straight-chain alkyl or alkoxy        having 1 to 6 C atoms or straight-chain alkenyl having 2 to 6 C        atoms, and    -   Z¹ and Z² each, independently of one another, denote —C₂H₄—,        —CH═CH—, —(CH₂)₄—, —(CH₂)₃O—, —O(CH₂)₃—, —CH═CH—CH₂CH₂—,        —CH₂CH₂CH═CH—, —CH₂O—, —OCH₂—, —CO—O—, —O—CO—, —C₂F₄—, —CF═CF—,        —CF═CH—, —CH═CF—, —CH₂— or a single bond.

-   n) The LC medium comprises one or more difluorodibenzochromans    and/or chromans of the following formulae:

-   -   in which    -   R¹¹ and R¹² each, independently of one another, have one of the        meanings indicated above for R¹¹,    -   ring M is trans-1,4-cyclohexylene or 1,4-phenylene,    -   Z^(m) —C₂H₄—, —CH₂O—, —OCH₂—, —CO—O— or —O—CO—,    -   c is 0, 1 or 2,    -   preferably in amounts of 3 to 20% by weight, in particular in        amounts of 3 to 15% by weight.    -   Particularly preferred compounds of the formulae BC, CR and RC        are selected from the group consisting of the following        sub-formulae:

-   -   in which alkyl and alkyl* each, independently of one another,        denote a straight-chain alkyl radical having 1-6 C atoms, (O)        denotes an oxygen atom or a single bond, c is 1 or 2, and        alkenyl and alkenyl* each, independently of one another, denote        a straight-chain alkenyl radical having 2-6 C atoms. Alkenyl and        alkenyl* preferably denote CH₂═CH—, CH₂═CHCH₂CH₂—, CH₃—CH═CH—,        CH₃—CH₂—CH═CH—, CH₃—(CH₂)₂—CH═CH—, CH₃—(CH₂)₃—CH═CH— or        CH₃—CH═CH—(CH₂)₂—.    -   Very particular preference is given to mixtures comprising one,        two or three compounds of the formula BC-2.

-   o) The LC medium comprises one or more fluorinated phenanthrenes    and/or dibenzofurans of the following formulae:

-   -   in which R¹¹ and R¹² each, independently of one another, have        one of the meanings indicated above for R¹¹, b denotes 0 or 1, L        denotes F, and r denotes 1, 2 or 3.    -   Particularly preferred compounds of the formulae PH and BF are        selected from the group consisting of the following        sub-formulae:

-   -   in which R and R′ each, independently of one another, denote a        straight-chain alkyl or alkoxy radical having 1-7 C atoms.

-   p) The LC medium comprises one or more monocyclic compounds of the    following formula

-   -   wherein    -   R¹ and R² each, independently of one another, denote alkyl        having 1 to 12 C atoms, where, in addition, one or two        non-adjacent CH₂ groups may be replaced by —O—, —CH═CH—, —CO—,        —OCO— or —COO— in such a way that O atoms are not linked        directly to one another, preferably alkyl or alkoxy having 1 to        6 C atoms,    -   L¹ and L² each, independently of one another, denote F, Cl,        OCF₃, CF₃, CH₃, CH₂F, CHF₂.    -   Preferably, both L¹ and L² denote F or one of L¹ and L² denotes        F and the other denotes Cl,    -   The compounds of the formula Y are preferably selected from the        group consisting of the following sub-formulae:

-   -   in which, Alkyl and Alkyl* each, independently of one another,        denote a straight-chain alkyl radical having 1-6 C atoms, Alkoxy        denotes a straight-chain alkoxy radical having 1-6 C atoms, and        Alkenyl and Alkenyl* each, independently of one another, denote        a straight-chain alkenyl radical having 2-6 C atoms. Alkenyl and        Alkenyl* preferably denote CH₂═CH—, CH₂═CHCH₂CH₂—, CH₃—CH═CH—,        CH₃—CH₂—CH═CH—, CH₃—(CH₂)₂—CH═CH—, CH₃—(CH₂)₃—CH═CH— or        CH₃—CH═CH—(CH₂)₂—.    -   Particularly preferred compounds of the formula Y are selected        from the group consisting of the following sub-formulae:

-   -   wherein Alkoxy preferably denotes straight-chain alkoxy with 3,        4, or 5 C atoms.

-   q) The LC medium comprises one or more quaterphenyl compounds    selected from the group consisting of the following formulae:

-   -   wherein    -   R^(Q) is alkyl, alkoxy, oxaalkyl or alkoxyalkyl having 1 to 9 C        atoms or alkenyl or alkenyloxy having 2 to 9 C atoms, all of        which are optionally fluorinated,    -   X^(Q) is F, Cl, halogenated alkyl or alkoxy having 1 to 6 C        atoms or halogenated alkenyl or alkenyloxy having 2 to 6 C        atoms,    -   L^(Q1) to L^(Q6) independently of each other are H or F, with at        least one of L^(Q1) to L^(Q6) being F.    -   Preferred compounds of formula Q are those wherein R^(Q) denotes        straight-chain alkyl with 2 to 6 C-atoms, very preferably ethyl,        n-propyl or n-butyl.    -   Preferred compounds of formula Q are those wherein L^(Q3) and        L^(Q4) are F. Further preferred compounds of formula Q are those        wherein L³, L^(Q4) and one or two of L^(Q1) and L^(Q2) are F.    -   Preferred compounds of formula Q are those wherein X^(Q) denotes        F or OCF₃, very preferably F.    -   The compounds of formula Q are preferably selected from the        following subformulae

-   -   wherein R^(Q) has one of the meanings of formula Q or one of its        preferred meanings given above and below, and is preferably        ethyl, n-propyl or n-butyl.    -   Especially preferred are compounds of formula Q1, in particular        those wherein R^(Q) is n-propyl.    -   Preferably the proportion of compounds of formula Q in the        mixture as a whole is from >0 to ≤5% by weight, very preferably        from 0.1 to 2% by weight, most preferably from 0.2 to 1.5% by        weight.    -   Preferably the LC medium contains 1 to 5, preferably 1 or 2        compounds of formula Q.    -   The addition of quaterphenyl compounds of formula Q to the LC        host mixture enables to reduce ODF mura, whilst maintaining high        UV absorption, enabling quick and complete polymerisation,        enabling strong and quick tilt angle generation, and increasing        the UV stability of the LC medium.    -   Besides, the addition of compounds of formula Q, which have        positive dielectric anisotropy, to the LC medium with negative        dielectric anisotropy allows a better control of the values of        the dielectric constants ε_(∥) and ε_(⊥), and in particular        enables to achieve a high value of the dielectric constant ε_(∥)        while keeping the dielectric anisotropy Δε constant, thereby        reducing the kick-back voltage and reducing image sticking.

-   r) the LC medium comprises one or more compounds of formula C:

-   -   wherein    -   R^(C) denotes alkyl, alkoxy, oxaalkyl or alkoxyalkyl having 1 to        9 C atoms or alkenyl or alkenyloxy having 2 to 9 C atoms, all of        which are optionally fluorinated,    -   X^(C) denotes F, Cl, halogenated alkyl or alkoxy having 1 to 6 C        atoms or halogenated alkenyl or alkenyloxy having 2 to 6 C        atoms,    -   L^(C1), L^(C2) independently of each other denote H or F, with        at least one of L^(C1) and L^(C2) being F.    -   Preferred compounds of formula C are those wherein R^(C) denotes        straight-chain alkyl with 2 to 6 C-atoms, very preferably ethyl,        n-propyl or n-butyl.    -   Preferred compounds of formula C are those wherein L^(C1) and        L^(C2) are F.    -   Preferred compounds of formula C are those wherein X^(C) denotes        F or OCF₃, very preferably F.    -   Preferred compounds of formula C are selected from the following        formula

-   -   wherein R^(C) has one of the meanings of formula C or one of its        preferred meanings given above and below, and is preferably        ethyl, n-propyl or n-butyl, very preferably n-propyl.    -   Preferably the proportion of compounds of formula C in the        mixture as a whole is from >0 to ≤10% by weight, very preferably        from 0.1 to 8% by weight, most preferably from 0.2 to 5% by        weight.    -   Preferably the LC medium contains 1 to 5, preferably 1, 2 or 3        compounds of formula C.    -   The addition of compounds of formula C, which have positive        dielectric anisotropy, to the LC medium with negative dielectric        anisotropy allows a better control of the values of the        dielectric constants ε_(∥) and ε_(⊥), and in particular enables        to achieve a high value of the dielectric constant ε_(∥) while        keeping the dielectric anisotropy Δε constant, thereby reducing        the kick-back voltage and reducing image sticking. Besides, the        addition of compounds of formula C enables to reduce the        viscosity and the response time of the LC medium.

-   s) The LC medium comprises 1 to 8, preferably 1 to 5, compounds of    the formulae CY1, CY2, PY1 and/or PY2. The proportion of these    compounds in the mixture as a whole is preferably 5 to 60%,    particularly preferably 10 to 35%. The content of these individual    compounds is preferably in each case 2 to 20%.

-   t) The LC medium comprises 1 to 8, preferably 1 to 5, compounds of    the formulae CY9, CY10, PY9 and/or PY10. The proportion of these    compounds in the mixture as a whole is preferably 5 to 60%,    particularly preferably 10 to 35%. The content of these individual    compounds is preferably in each case 2 to 20%.

-   u) The LC medium comprises 1 to 10, preferably 1 to 8, compounds of    the formula ZK, in particular compounds of the formulae ZK1, ZK2    and/or ZK6. The proportion of these compounds in the mixture as a    whole is preferably 3 to 25%, particularly preferably 5 to 45%. The    content of these individual compounds is preferably in each case 2    to 20%.

-   v) In the LC medium the proportion of compounds of formulae CY, PY    and ZK in the mixture as a whole is greater than 70%, preferably    greater than 80%.

-   w) The LC medium contains one or more compounds containing an    alkenyl group, preferably selected from the group consisting of    formula CY, PY and DY, wherein one or both of R¹ and R² denote    straight-chain alkenyl having 2-6 C atoms, formula ZK and DK,    wherein one or both of R³ and R⁴ or one or both of R⁵ and R⁶ denote    straight-chain alkenyl having 2-6 C atoms, and formula B2 and B3,    very preferably selected from formulae CY15, CY16, CY24, CY32, PY15,    PY16, ZK3, ZK4, DK3, DK6, B2 and B3. The concentration of these    compounds in the LC host mixture is preferably from 2 to 70%, very    preferably from 3 to 55%.

-   x) The LC medium contains one or more, preferably 1 to 5, compounds    selected of formula PY1-PY8, very preferably of formula PY2. The    proportion of these compounds in the mixture as a whole is    preferably 1 to 30%, particularly preferably 2 to 20%. The content    of these individual compounds is preferably in each case 1 to 20%.

-   y) The L medium contains one or more compounds selected from    formulae AN1 to AN15, preferably from AN1, AN3 and AN6, more    preferably from formulae AN1a and AN6a, very preferably from    formulae AN1a2, AN1a5, AN6a1 and AN6a2. The proportion of these    compounds in the mixture as a whole is preferably from 5 to 70%,    more preferably from 10 to 60%, most preferably from 20 to 60%.

-   z) The L medium contains one or more compounds selected from    formulae AY1 to AY14, more preferably from formulae AY5a, AY6a,    AY9a, AY10a, AY11a and AY14a, very preferably from formula AY14a.    The proportion of these compounds in the mixture as a whole is    preferably from 2 to 50% by weight, very preferably from 5 to 40% by    weight, most preferably from 5 to 30% by weight.

The combination of compounds of the preferred embodiments mentionedabove with the polymerised compounds described above causes lowthreshold voltages, low rotational viscosities and very goodlow-temperature stabilities in the LC media according to the inventionat the same time as constantly high clearing points and high VHR values.

The use of LC media containing polymerisable compounds allows the rapidestablishment of a particularly low pretilt angle in PSA displays. Inparticular, the LC media exhibit significantly shortened response times,in particular also the grey-shade response times, in PSA displayscompared with the media from the prior art.

The LC media and LC host mixtures of the present invention preferablyhave a nematic phase range of at least 80 K, particularly preferably atleast 100 K, and a rotational viscosity≤250 mPa·s, preferably ≤200mPa·s, at 20° C.

In the VA-type displays according to the invention, the molecules in thelayer of the LC medium in the switched-off state are alignedperpendicular to the electrode surfaces (homeotropically) or have a atilted homeotropic alignment. On application of an electrical voltage tothe electrodes, a realignment of the LC molecules takes place with thelongitudinal molecular axes parallel to the electrode surfaces.

The LC media according to the invention are preferably based oncompounds with negative dielectric anisotropy, are in particularsuitable for use in displays of the VA, UB-FFS, PS-VA and PS-UB-FFStype, and preferably have a negative dielectric anisotropy Δε, verypreferably from −0.5 to −10, most preferably from −2.5 to −7.5, at 20°C. and 1 kHz.

The birefringence Δn in LC media according to the invention, especiallyfor use in displays of the VA, UB-FFS, PS-VA and PS-UB-FFS type, ispreferably below 0.16, particularly preferably from 0.06 to 0.14, veryparticularly preferably from 0.07 to 0.12.

The LC media according to the invention may also comprise furtheradditives which are known to the person skilled in the art and aredescribed in the literature, such as, for example, polymerisationinitiators, inhibitors, stabilisers, surface-active substances or chiraldopants. These may be polymerisable or non-polymerisable.

In a preferred embodiment of the present invention the LC mediumadditionally comprises one or more polymerisable compounds.

The polymerisable compounds are preferably selected from formula M

R^(a)—B¹—(Z^(b)—B²)_(m)—R^(b)  M

in which the individual radicals, on each occurrence identically ordifferently, and each, independently of one another, have the followingmeaning:

-   R^(a) and R^(b) P, P-Sp-, H, F, Cl, Br, I, —CN, —NO₂, —NCO, —NCS,    —OCN, —SCN, SF₅ or straight-chain or branched alkyl having 1 to 25 C    atoms, in which, in addition, one or more non-adjacent CH₂ groups    may each be replaced, independently of one another, by    —C(R⁰)═C(R⁰⁰)—, —C≡C—, —N(R⁰⁰)—, —O—, —S—, —CO—, —CO—O—, —O—CO—,    —O—CO—O— in such a way that O and/or S atoms are not linked directly    to one another, and in which, in addition, one or more H atoms may    be replaced by F, Cl, Br, I, CN, P or P-Sp-, where, if B¹ and/or B²    contain a saturated C atom, R^(a) and/or R^(b) may also denote a    radical which is spiro-linked to this saturated C atom,-   wherein at least one of the radicals R^(a) and R^(b) denotes or    contains a group P or P-Sp-,-   P a polymerisable group,-   Sp a spacer group or a single bond,-   B¹ and B² an aromatic, heteroaromatic, alicyclic or heterocyclic    group, preferably having 4 to 25 ring atoms, which may also contain    fused rings, and which is unsubstituted, or mono- or polysubstituted    by L,-   Z^(b) —O—, —S—, —CO—, —CO—O—, —OCO—, —O—CO—O—, —OCH₂—, —CH₂O—,    —SCH₂—, —CH₂S—, —CF₂O—, —OCF₂—, —CF₂S—, —SCF₂—, —(CH₂)_(n1)—,    —CF₂CH₂—, —CH₂CF₂—, —(CF₂)_(n1)—, —CH═CH—, —CF═CF—, —C≡C—,    —CH═CH—COO—, —OCO—CH═CH—, CR⁰R⁰⁰ or a single bond,-   R⁰ and R⁰⁰ each, independently of one another, denote H or alkyl    having 1 to 12 C atoms,-   m denotes 0, 1, 2, 3 or 4,-   n1 denotes 1, 2, 3 or 4,-   L P, P-Sp-, OH, CH₂OH, F, Cl, Br, I, —CN, —NO₂, —NCO, —NCS, —OCN,    —SCN, —C(═O)N(R^(x))₂, —C(═O)Y¹, —C(═O)R^(x), —N(R^(x))₂, optionally    substituted silyl, optionally substituted aryl having 6 to 20 C    atoms, or straight-chain or branched alkyl, alkoxy, alkylcarbonyl,    alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy having 1 to 25    C atoms, in which, in addition, one or more H atoms may be replaced    by F, Cl, P or P-Sp-,-   P and Sp have the meanings indicated above,-   Y¹ denotes halogen,-   R^(x) denotes P, P-Sp-, H, halogen, straight-chain, branched or    cyclic alkyl having 1 to 25 C atoms, in which, in addition, one or    more non-adjacent CH₂ groups may be replaced by —O—, —S—, —CO—,    —CO—O—, —O—CO—, —O—CO—O— in such a way that O and/or S atoms are not    linked directly to one another, and in which, in addition, one or    more H atoms may be replaced by F, Cl, P or P-Sp-, an optionally    substituted aryl or aryloxy group having 6 to 40 C atoms, or an    optionally substituted heteroaryl or heteroaryloxy group having 2 to    40 C atoms.

Particularly preferred compounds of the formula I are those in which B¹and B² each, independently of one another, denote 1,4-phenylene,1,3-phenylene, naphthalene-1,4-diyl, naphthalene-2,6-diyl,phenanthrene-2,7-diyl, 9,10-dihydro-phenanthrene-2,7-diyl,anthracene-2,7-diyl, fluorene-2,7-diyl, coumarine, flavone, where, inaddition, one or more CH groups in these groups may be replaced by N,cyclohexane-1,4-diyl, in which, in addition, one or more non-adjacentCH₂ groups may be replaced by O and/or S, 1,4-cyclohexenylene,bicycle[1.1.1]pentane-1,3-diyl, bicyclo[2.2.2]octane-1,4-diyl,spiro[3.3]heptane-2,6-diyl, piperidine-1,4-diyl,decahydronaphthalene-2,6-diyl, 1,2,3,4-tetrahydronaphthalene-2,6-diyl,indane-2,5-diyl or octahydro-4,7-methanoindane-2,5-diyl, where all thesegroups may be unsubstituted or mono- or polysubstituted by L as definedabove.

Particularly preferred compounds of the formula M are those in which B¹and B² each, independently of one another, denote 1,4-phenylene,1,3-phenylene, naphthalene-1,4-diyl or naphthalene-2,6-diyl,

Very preferred compounds of formula M are selected from the followingformulae:

in which the individual radicals, on each occurrence identically ordifferently, and each, independently of one another, have the followingmeaning:

-   P¹, P², P³ a polymerisable group, preferably selected from vinyloxy,    acrylate, methacrylate, fluoroacrylate, chloroacrylate, oxetane and    epoxy,-   Sp¹, Sp², Sp³ a single bond or a spacer group where, in addition,    one or more of the radicals P¹-Sp¹-, P¹-Sp²- and P³-Sp³- may denote    R^(aa), with the proviso that at least one of the radicals P¹-Sp-,    P²-Sp² and P³-Sp³- present is different from R^(aa), preferably    —(CH₂)_(p1)—, —(CH₂)_(p1)—O—, —(CH₂)_(p1)—CO—O— or    —(CH₂)_(p1)—O—CO—O— bedeuten, wherein p1 is an integer from 1 to 12,-   R^(aa) H, F, Cl, CN or straight-chain or branched alkyl having 1 to    25 C atoms, in which, in addition, one or more non-adjacent CH₂    groups may each be replaced, independently of one another, by    —C(R⁰)═C(R⁰⁰)—, —C≡C—, —N(R⁰)—, —O—, —S—, —CO—, —CO—O—, —O—CO—,    —O—CO—O— in such a way that O and/or S atoms are not linked directly    to one another, and in which, in addition, one or more H atoms may    be replaced by F, Cl, CN or P¹-Sp¹-, particularly preferably    straight-chain or branched, optionally mono- or polyfluorinated    alkyl, alkoxy, alkenyl, alkynyl, alkylcarbonyl, alkoxycarbonyl,    alkylcarbonyloxy or alkoxycarbonyloxy having 1 to 12 C atoms (where    the alkenyl and alkynyl radicals have at least two C atoms and the    branched radicals have at least three C atoms),-   R⁰, R⁰⁰ H or alkyl having 1 to 12 C atoms,-   R^(y) and R^(z) H, F, CH₃ or CF₃,-   X¹, X², X³ —CO—O—, —O—CO— or a single bond,-   Z^(M1) —O—, —CO—, —C(R^(y)R^(z))— or —CF₂CF₂—,-   Z^(M2), Z^(M3) —CO—O—, —O—CO—, —CH₂O—, —OCH₂—, —CF₂O—, —OCF₂— or    —(CH₂)_(n)—, where n is 2, 3 or 4,-   L F, Cl, CN or straight-chain or branched, optionally mono- or    polyfluorinated alkyl, alkoxy, alkenyl, alkynyl, alkylcarbonyl,    alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy having 1 to 12    C atoms,-   L′, L″ H, F or Cl,-   k 0 or 1,-   r 0, 1, 2, 3 or 4,-   s 0, 1, 2 or 3,-   t 0, 1 or 2,-   x 0 or 1.

Especially preferred are compounds of formulae M2 and M13.

Further preferred are trireactive compounds M15 to M31, in particularM17, M18, M19, M22, M23, M24, M25, M30, M31 and M32.

In the compounds of formulae M1 to M32 the group

is preferably

wherein L on each occurrence, identically or differently, has one of themeanings given above or below, and is preferably F, Cl, CN, NO₂, CH₃,C₂H₅, C(CH₃)₃, CH(CH₃)₂, CH₂CH(CH₃)C₂H₅, OCH₃, OC₂H₅, COCH₃, COC₂H₅,COOCH₃, COOC₂H₅, CF₃, OCF₃, OCHF₂, OC₂F₅ or P-Sp-, very preferably F,Cl, CN, CH₃, C₂H₅, OCH₃, COCH₃, OCF₃ or P-Sp-, more preferably F, Cl,CH₃, OCH₃, COCH₃ oder OCF₃, especially F or CH₃.

Preferred compounds of formulae M1 to M32 are those wherein P¹, P² andP³ denote an acrylate, methacrylate, oxetane or epoxy group, verypreferably an acrylate or methacrylate group.

Further preferred compounds of formulae M1 to M32 are those wherein Sp¹,Sp² and Sp³ are a single bond.

Further preferred compounds of formulae M1 to M32 are those wherein oneof Sp¹, Sp² and Sp³ is a single bond and another one of Sp¹, Sp² and Sp³is different from a single bond.

Further preferred compounds of formulae M1 to M32 are those whereinthose groups Sp¹, Sp² and Sp³ that are different from a single bonddenote —(CH₂)_(s1)—X″—, wherein s1 is an integer from 1 to 6, preferably2, 3, 4 or 5, and X″ is X″ is the linkage to the benzene ring and is—O—, —O—CO—, —CO—O—, —O—CO—O— or a single bond.

Particular preference is given to LC media comprising one, two or threepolymerisable compounds of formula M, preferably selected from formulaeM1 to M32.

Further preferred polymerisable compounds are listed in Table D below.

Preferably the proportion of polymerisable compounds in the LC medium isfrom 0.01 to 5%, very preferably from 0.05 to 1%, most preferably from0.1 to 0.5%.

The polymerisable group P is a group which is suitable for apolymerisation reaction, such as, for example, free-radical or ionicchain polymerisation, polyaddition or polycondensation, or for apolymer-analogous reaction, for example addition or condensation onto amain polymer chain. Particular preference is given to groups for chainpolymerisation, in particular those containing a C═C double bond or—C≡C— triple bond, and groups which are suitable for polymerisation withring opening, such as, for example, oxetane or epoxide groups.

Preferred groups P are selected from the group consisting ofCH₂═CW¹—CO—O—, CH₂═CW¹—CO—,

CH₂═CW²—(O)_(k3)—, CW¹═CH—CO—(O)_(k3)—, CW¹═CH—CO—NHCH₂═CW¹—CO—NH—,CH₃—CH═CH—O—, (CH₂═CH)₂CH—OCO—, (CH₂═CHCH₂)₂CH—OCO—, (CH₂═CH)₂CH—O—,(CH₂═CH—CH₂)₂N—, (CH₂═CH—CH₂)₂N—CO—, HO—CW²W³—, HS—CW²W³—, HW²N—,HO—CW²W³—NH—, CH₂═CW¹—CO—NH, CH₂═CH—(COO)_(k1)-Phe-(O)_(k2)—,CH₂═CH—(CO)_(k1)-Phe-(O)_(k2)—, Phe-CH═CH—, HOOC—, OCN— and W⁴W⁵W⁶Si—,in which W¹ denotes H, F, Cl, CN, CF₃, phenyl or alkyl having 1 to 5 Catoms, in particular H, F, Cl or CH₃, W² and W³ each, independently ofone another, denote H or alkyl having 1 to 5 C atoms, in particular H,methyl, ethyl or n-propyl, W⁴, W⁵ and W⁶ each, independently of oneanother, denote Cl, oxaalkyl or oxacarbonylalkyl having 1 to 5 C atoms,W⁷ and W⁸ each, independently of one another, denote H, Cl or alkylhaving 1 to 5 C atoms, Phe denotes 1,4-phenylene, which is optionallysubstituted by one or more radicals L as defined above which are otherthan P-Sp-, k₁, k₂ and k₃ each, independently of one another, denote 0or 1, k₃ preferably denotes 1, and k₄ denotes an integer from 1 to 10.

Very preferred groups P are selected from the group consisting ofCH₂═CW¹—CO—O—, CH₂═CW¹—CO—,

CH₂═CW²—O—, CH₂═CW²—, CW¹═CH—CO—(O)_(k3)—, CW¹═CH—CO—NH—,CH₂═CW¹—CO—NH—, (CH₂═CH)₂CH—OCO—, (CH₂═CH—CH₂)₂CH—OCO—, (CH₂═CH)₂CH—O—,(CH₂═CH—CH₂)₂N—, (CH₂═CH—CH₂)₂N—CO—, CH₂═CW¹—CO—NH—,CH₂═CH—(COO)_(k1)-Phe-(O)_(k2)—, CH₂═CH—(CO)_(k1)-Phe-(O)_(k2)—,Phe-CH═CH— and W⁴W⁵W⁶Si—, in which W¹ denotes H, F, Cl, CN, CF₃, phenylor alkyl having 1 to 5 C atoms, in particular H, F, Cl or CH₃, W² and W³each, independently of one another, denote H or alkyl having 1 to 5 Catoms, in particular H, methyl, ethyl or n-propyl, W⁴, W⁵ and W⁶ each,independently of one another, denote Cl, oxaalkyl or oxacarbonylalkylhaving 1 to 5 C atoms, W⁷ and W⁸ each, independently of one another,denote H, Cl or alkyl having 1 to 5 C atoms, Phe denotes 1,4-phenylene,k₁, k₂ and k₃ each, independently of one another, denote 0 or 1, k₃preferably denotes 1, and k₄ denotes an integer from 1 to 10.

Very particularly preferred groups P are selected from the groupconsisting of CH₂═CW¹—CO—O—, in particular CH₂═CH—CO—O—,CH₂═C(CH₃)—CO—O— and CH₂═CF—CO—O—, furthermore CH₂═CH—O—,(CH₂═CH)₂CH—O—CO—, (CH₂═CH)₂CH—O—,

Further preferred polymerisable groups P are selected from the groupconsisting of vinyloxy, acrylate, methacrylate, fluoroacrylate,chloroacrylate, oxetane and epoxide, most preferably from acrylate andmethacrylate.

If Sp is different from a single bond, it is preferably of the formulaSp″-X″, so that the respective radical P-Sp- conforms to the formulaP-Sp″-X″—, wherein

-   Sp″ denotes alkylene having 1 to 20, preferably 1 to 12, C atoms,    which is optionally mono- or polysubstituted by F, Cl, Br, I or CN    and in which, in addition, one or more non-adjacent CH₂ groups may    each be replaced, independently of one another, by —O—, —S—, —NH—,    —N(R⁰)—, —Si(R⁰R⁰⁰)—, —CO—, —CO—O—, —O—CO—, —O—CO—O—, —S—CO—,    —CO—S—, —N(R⁰⁰)—CO—O—, —O—CO—N(R⁰)—, —N(R⁰)—CO—N(R⁰⁰)—, —CH═CH— or    —C≡C— in such a way that O and/or S atoms are not linked directly to    one another,-   X″ denotes —O—, —S—, —CO—, —CO—O—, —O—CO—, —O—CO—O—, —CO—N(R)—,    —N(R⁰)—CO—, —N(R⁰)—CO—N(R⁰⁰)—, —OCH₂—, —CH₂O—, —SCH₂—, —CH₂S,    —CF₂O—, —OCF₂—, —CF₂S—, —SCF₂—, —CF₂CH₂—, —CH₂CF₂—, —CF₂CF₂—,    —CH═N—, —N═CH—, —N═N—, —CH═CR⁰—, —CY²═CY³—, —C≡C—, —CH═CH—CO—O—,    —O—CO—CH═CH— or a single bond,-   R⁰ and R⁰⁰ each, independently of one another, denote H or alkyl    having 1 to 20 C atoms, and-   Y² and Y³ each, independently of one another, denote H, F, Cl or CN.

X is preferably —O—, —S—, —CO—, —COO—, —OCO—, —O—COO—, —CO—NR⁰—,—NR⁰—CO—, —NR⁰—CO—NR⁰⁰— or a single bond.

Typical spacer groups Sp and -Sp″-X″— are, for example, —(CH₂)_(p1)—,—(CH₂CH₂O)_(q1)—CH₂CH₂—, —CH₂CH₂—S—CH₂CH₂—, —CH₂CH₂—NH—CH₂CH₂— or—(SiR⁰R⁰⁰—O)_(p1)—, in which p1 is an integer from 1 to 12, q1 is aninteger from 1 to 3, and R⁰ and R⁰⁰ have the meanings indicated above.

Particularly preferred groups Sp and -Sp″-X″— are —(CH₂)_(p1)—,—(CH₂)_(p1)—O—, —(CH₂)_(p1)—O—CO—, —(CH₂)_(p1)—CO—O—,—(CH₂)_(p1)—O—CO—O—, in which p1 and q1 have the meanings indicatedabove.

Particularly preferred groups Sp″ are, in each case straight-chain,ethylene, propylene, butylene, pentylene, hexylene, heptylene, octylene,nonylene, decylene, undecylene, dodecylene, octadecylene,ethyleneoxyethylene, methyleneoxybutylene, ethylenethioethylene,ethylene-N-methyliminoethylene, 1-methylalkylene, ethenylene,propenylene and butenylene.

For the production of PSA displays, the polymerisable compoundscontained in the LC medium are polymerised or crosslinked (if onecompound contains two or more polymerisable groups) by in-situpolymerisation in the LC medium between the substrates of the LCdisplay, optionally while a voltage is applied to the electrodes.

The structure of the PSA displays according to the invention correspondsto the usual geometry for PSA displays, as described in the prior artcited at the outset. Geometries without protrusions are preferred, inparticular those in which, in addition, the electrode on the colorfilter side is unstructured and only the electrode on the TFT side hasslots. Particularly suitable and preferred electrode structures forPS-VA displays are described, for example, in US 2006/0066793 A1.

Preferably the proportion of the polymerisable compounds in the LCmedium is from >0 to <5%, very preferably from >0 to <1%, mostpreferably from 0.01 to 0.5%.

Optionally one or more polymerisation initiators are added to the LCmedium. Suitable conditions for the polymerisation and suitable typesand amounts of initiators are known to the person skilled in the art andare described in the literature. Suitable for free-radicalpolymerisation are, for example, the commercially availablephotoinitiators Irgacure651@, Irgacure184@, Irgacure907, Irgacure369@ orDarocure1173@ (Ciba AG). If a polymerisation initiator is employed, itsproportion is preferably 0.001 to 5% by weight, particularly preferably0.001 to 1% by weight.

In another preferred embodiment the LC medium does not contain apolymerisation initiator.

The LC medium may also comprise one or more stabilisers. Suitable typesand amounts of stabilisers are known to the person skilled in the artand are described in the literature. Particularly suitable are, forexample, the commercially available stabilisers from the Irganox® series(Ciba AG), such as, for example, Irganox®1076. If stabilisers areemployed, their proportion is preferably 10-500,000 ppm, more preferably50-5,000 ppm, very preferably 50-1,000 ppm.

In another preferred embodiment of the present invention the LC mediumcontains one or more stabilisers selected from Table C below.

In another preferred embodiment of the present invention the LC mediumcontains one or more stabilisers selected from the the group consistingof the following formulae

wherein the individual radicals, independently of each other and on eachoccurrence identically or differently, have the following meanings

-   R^(a-d) straight-chain or branched alkyl with 1 to 10, preferably 1    to 6, very preferably 1 to 4 C atoms, most preferably methyl,-   X^(S) H, CH₃, OH or O.,-   A^(S) straight-chain, branched or cyclic alkylene with 1 to 20 C    atoms which is optionally substituted,-   n an integer from 1 to 6, preferably 3.

Preferred stabilisers of formula S3 are selected from formula S3A

wherein n2 is an integer from 1 to 12, and wherein one or more H atomsin the group (CH₂)_(n2) are optionally replaced by methyl, ethyl,propyl, butyl, pentyl or hexyl.

Very preferred stabilisers are selected from the group consisting of thefollowing formulae

In a preferred embodiment the liquid-crystalline medium comprises one ormore stabilisers selected from the group consisting of formulae S1-1,S2-1, S3-1, S3-1 and S3-3.

In a preferred embodiment the liquid-crystalline medium comprises one ormore stabilisers selected from Table C below.

Preferably the proportion of stabilisers, like those of formula S1-S3,in the liquid-crystalline medium is from 10 to 500 ppm, very preferablyfrom 20 to 100 ppm.

In another preferred embodiment the LC medium according to the presentinvention contains one or more SA additives selected from formula II orits subformulae. The concentration of the SA additives in the LC mediumis preferably from 0.1 to 5%, very preferably from 0.2 to 3%, mostpreferably from 0.2 to 1.5%.

In a preferred embodiment the LC medium or display according to thepresent invention contains one or more SA additives selected from TableF below.

In another preferred embodiment the SA-VA or SA-FFS display according tothe present invention does not contain a polyimide alignment layer.

Preference is given to LC media which have a nematic LC phase, andpreferably have no chiral liquid crystal phase.

In another preferred embodiment the LC media contain one or more chiraldopants, preferably in a concentration from 0.01 to 1%, very preferablyfrom 0.05 to 0.5%. The chiral dopants are preferably selected from thegroup consisting of compounds from Table B below, very preferably fromthe group consisting of R- or S-1011, R- or S-2011, R- or S-3011, R- orS-4011, and R- or S-5011.

In another preferred embodiment the LC media contain a racemate of oneor more chiral dopants, which are preferably selected from the chiraldopants mentioned in the previous paragraph.

Furthermore, it is possible to add to the LC media, for example, 0 to15% by weight of pleochroic dyes, furthermore nanoparticles, conductivesalts, preferably ethyldimethyldodecylammonium 4-hexoxybenzoate,tetrabutylammonium tetraphenylborate or complex salts of crown ethers(cf., for example, Haller et al., Mol. Cryst. Liq. Cryst. 24, 249-258(1973)), for improving the conductivity, or substances for modifying thedielectric anisotropy, the viscosity and/or the alignment of the nematicphases. Substances of this type are described, for example, in DE-A 2209 127, 22 40 864, 23 21 632, 23 38 281, 24 50 088, 26 37 430 and 28 53728.

The individual components of the preferred embodiments a)-z) of the LCmedia according to the invention are either known or methods for thepreparation thereof can readily be derived from the prior art by theperson skilled in the relevant art, since they are based on standardmethods described in the literature. Corresponding compounds of theformula CY are described, for example, in EP-A-0 364 538. Correspondingcompounds of the formula ZK are described, for example, in DE-A-26 36684 and DE-A-33 21 373.

The LC media which can be used in accordance with the invention areprepared in a manner conventional per se, for example by mixing one ormore of the above-mentioned compounds with one or more polymerisablecompounds as defined above, and optionally with furtherliquid-crystalline compounds and/or additives. In general, the desiredamount of the components used in lesser amount is dissolved in thecomponents making up the principal constituent, advantageously atelevated temperature. It is also possible to mix solutions of thecomponents in an organic solvent, for example in acetone, chloroform ormethanol, and to remove the solvent again, for example by distillation,after thorough mixing. The invention furthermore relates to the processfor the preparation of the LC media according to the invention.

It goes without saying to the person skilled in the art that the LCmedia according to the invention may also comprise compounds in which,for example, H, N, O, Cl, F have been replaced by the correspondingisotopes like deuterium etc.

The construction of an LC display according to the invention frompolarisers, electrode base plates and surface-treated electrodescorresponds to the usual design for displays of this type. The termusual design is broadly drawn here and also encompasses all derivativesand modifications of the LC display, in particular including matrixdisplay elements based on poly-Si TFTs or MIM.

The following examples explain the present invention without restrictingit. However, they show the person skilled in the art preferred mixtureconcepts with compounds preferably to be employed and the respectiveconcentrations thereof and combinations thereof with one another. Inaddition, the examples illustrate which properties and propertycombinations are accessible.

Above and below, percentage data denote percent by weight; alltemperatures are indicated in degrees Celsius.

Throughout the patent application and in the working examples, thestructures of the liquid-crystal compounds are indicated by means ofacronyms. Unless indicated otherwise, the transformation into chemicalformulae takes place in accordance with Tables I-III. All radicalsC_(n)H_(2c+1), C_(m)H_(2m+1), C_(n)H_(2n), C_(m)H_(2m) and C_(k)H_(2k)are straight-chain alkyl radicals or alkenyl radicals respectively, ineach case having n, m or k C atoms; n and m each, independently of oneanother, denote 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12, preferably 1,2, 3, 4, 5 or 6, and k is 0, 1, 2, 3, 4, 5 or 6. In Table I the ringelements of the respective compound are coded, in Table the bridgingmembers are listed and in Table III the meanings of the symbols for theleft-hand and right-hand side chains of the compounds are indicated.

TABLE I Ring elements

A

AI

B

B(S)

C

D

DI

F

FI

G

GI

K

L

LI

M

MI

N

NI

P

S

U

UI

Y

Y(F, Cl)

Y(Cl, F)

TABLE II Bridging members E —CH₂CH₂— V —CH═CH— T —C≡C— W —CF₂CF₂— Z—COO— ZI —OCO— O —CH₂O— OI —OCH₂— Q —CF₂O— QI —OCF₂—

TABLE III Side chains Left-hand side chain Right-hand side chain n-C_(n)H_(2n+1)— -n —C_(n)H_(2n+1) nO- C_(n)H_(2n+1)—O— -On—O—C_(n)H_(2n+1) V— CH₂═ CH— —V —CH═CH₂ nV- C_(n)H_(2n+1)—CH═CH— -nV—C_(n)H_(2n)—CH═CH₂ Vn- CH₂═CH—C_(n)H_(2n)— -Vn —CH═CH—C_(n)H_(2n+1)nVm- C_(n)H_(2n+1)—CH═CH—C_(m)H_(2m)— -nVm—C_(n)H_(2n)—CH═CH—C_(m)H_(2m+1) N— N≡C— —N —C≡N F— F— —F —F Cl— Cl— —Cl—Cl M- CFH₂— -M —CFH₂ D- CF₂H— -D —CF₂H T- CF₃— -T —CF₃ MO- CFH₂O— -OM—OCFH₂ DO- CF₂HO— -OD —OCF₂H TO- CF₃O— -OT —OCF₃ T- CF₃— -T —CF₃ A-H—C≡C— -A —C≡C—H FXO- CF₂═CHO— -OXF —OCH═CF₂

Preferred mixture components are shown in Table A.

TABLE A In the formulae below m and n are independently of each other aninteger from 1 to 12, preferably 1, 2, 3, 4, 5 or 6, k is 0, 1, 2, 3, 4,5 or 6, and (O)C_(m)H_(2m+1) means C_(m)H_(2m+1) or OC_(m)H_(2m+1).

Particular preference is given to liquid-crystalline mixtures whichcomprise at least one, two, three, four or more compounds from Table A.

Table B indicates possible dopants which are generally added to themixtures according to the invention. The mixtures preferably comprise0-10% by weight, in particular 0.001-5% by weight and particularlypreferably 0.001-3% by weight, of dopants.

TABLE B

TABLE C Stabilisers which can be added, for example, to the mixturesaccording to the invention in amounts of 0-10% by weight are mentionedbelow.

TABLE D Table D shows illustrative reactive mesogenic compounds whichcan be used in the LC media in accordance with the present invention.

RM-1

RM-2

RM-3

RM-4

RM-5

RM-6

RM-7

RM-8

RM-9

RM-10

RM-11

RM-12

RM-13

RM-14

RM-15

RM-16

RM-17

RM-18

RM-19

RM-20

RM-21

RM-22

RM-23

RM-24

RM-25

RM-26

RM-27

RM-28

RM-29

RM-30

RM-31

RM-32

RM-33

RM-34

RM-35

RM-36

RM-37

RM-38

RM-39

RM-40

RM-41

RM-42

RM-43

RM-44

RM-45

RM-46

RM-47

RM-48

RM-49

RM-50

RM-51

RM-52

RM-53

RM-54

RM-55

RM-56

RM-57

RM-58

RM-59

RM-60

RM-61

RM-62

RM-63

RM-64

RM-65

RM-66

RM-67

RM-68

RM-69

RM-70

RM-71

RM-72

RM-73

RM-74

RM-75

RM-76

RM-77

RM-78

RM-79

RM-80

RM-81

RM-82

RM-83

RM-84

RM-85

RM-86

RM-87

RM-88

RM-89

RM-90

RM-91

RM-92

RM-93

RM-94

RM-95

RM-96

RM-97

RM-98

RM-99

RM-100

RM-101

RM-102

RM-103

RM-104

RM-105

RM-106

RM-107

RM-108

RM-109

RM-110

RM-111

RM-112

RM-113

RM-114

RM-115

RM-116

RM-117

RM-118

RM-119

RM-120

RM-121

RM-122

RM-123

RM-124

RM-125

RM-126

RM-127

RM-128

RM-129

RM-130

RM-131

RM-132

RM-133

RM-134

RM-135

RM-136

RM-137

RM-138

RM-139

RM-140

RM-141

RM-142

RM-143

RM-144

RM-145

In a preferred embodiment, the mixtures according to the inventioncomprise one or more polymerizable compounds, preferably selected fromthe polymerizable compounds of the formulae RM-1 to RM-140. Of these,compounds RM-1, RM-4, RM-8, RM-17, RM-19, RM-35, RM-37, RM-39, RM-40,RM-41, RM-42, RM-50, RM-53, RM-54, RM-56, RM-59, RM-66, RM-76, RM-78,RM-90, RM-93, RM-104, RM-105, RM-111, RM-119, RM-122, RM-123 and RM-124are particularly preferred.

TABLE E Table E shows self-alignment additives for vertical alignmentwhich can be used in LC media for SA-VA and SA-FFS displays according tothe present invention together with the polymerizable compounds offormula I:

SA-1

SA-2

SA-3

SA-4

SA-5

SA-6

SA-7

SA-8

SA-9

SA-10

SA-11

SA-12

SA-13

SA-14

SA-15

SA-16

SA-17

SA-18

SA-19

SA-20

SA-21

SA-22

SA-23

SA-24

SA-25

SA-26

SA-27

SA-28

SA-29

SA-30

SA-31

SA-32

SA-33

SA-34

SA-35

SA-36

SA-37

SA-38

SA-39

SA-40

SA-41

SA-42

SA-43

SA-44

SA-45

SA-46

SA-47

SA-48

In a preferred embodiment, the LC media and displays according to thepresent invention comprise one or more SA additives selected fromformulae SA-1 to SA-48, preferably from formulae SA-14 to SA-48, verypreferably from formulae SA-20 to SA-34 and SA-48, preferably incombination with one or more RMs of formula M.

The following examples are intended to explain the invention withoutlimiting it.

Without further elaboration, it is believed that one skilled in the artcan, using the preceding description, utilize the present invention toits fullest extent. The preceding preferred specific embodiments are,therefore, to be construed as merely illustrative, and not limitative ofthe remainder of the disclosure in any way whatsoever.

The entire disclosures of all applications, patents and publications,cited herein and of corresponding European application No. 19171252.0,filed Apr. 26, 2019, are incorporated by reference herein.

Above and below, unless explicitly noted otherwise, all percentage datadenote percent by weight, and relate to the corresponding mixture as awhole, comprising all solid or liquid-crystalline components, withoutsolvents. Furthermore, unless explicitly noted otherwise, alltemperatures are indicated in in degrees Celsius (° C.). m.p. denotesmelting point, cl.p.=clearing point. Furthermore, C=crystalline state,N=nematic phase, S=smectic phase and I=isotropic phase. The data betweenthese symbols represent the transition temperatures.

In addition, the following abbreviations and symbols are used:

-   V₀ threshold voltage, capacitive [V] at 20° C.,-   n_(e) extraordinary refractive index at 20° C. and 589 nm,-   n_(o) ordinary refractive index at 20° C. and 589 nm,-   Δn optical anisotropy at 20° C. and 589 nm,-   ε_(⊥) dielectric permittivity perpendicular to the director at    20° C. and 1 kHz,-   ε_(∥) dielectric permittivity parallel to the director at 20° C. and    1 kHz,-   Δε dielectric anisotropy at 20° C. and 1 kHz,-   cl.p., T_(ni) clearing point [° C.],-   γ₁ rotational viscosity at 20° C. [mPa·s],-   K₁ elastic constant, “splay” deformation at 20° C. [pN],-   K₂ elastic constant, “twist” deformation at 20° C. [pN],-   K₃ elastic constant, “bend” deformation at 20° C. [pN].

All physical properties are and have been determined in accordance with“Merck Liquid Crystals, Physical Properties of Liquid Crystals”, StatusNovember 1997, Merck KGaA, Germany, and apply for a temperature of 20°C. unless explicitly indicated otherwise in each case.

The term “threshold voltage” for the present invention relates to thecapacitive threshold (V₀), also known as the Freedericks threshold,unless explicitly indicated otherwise. In the examples, the opticalthreshold may also, as generally usual, be quoted for 10% relativecontrast (V₁₀).

EXAMPLES

Unless stated otherwise, methods of preparing test cells and measuringtheir electrooptical and other properties are carried out by the methodsas described hereinafter or in analogy thereto.

The display used for measurement of the capacitive threshold voltageconsists of two plane-parallel glass outer plates at a separation of 25μm, each of which has on the inside an electrode layer and an unrubbedpolyimide alignment layer on top, which effect a homeotropic edgealignment of the liquid-crystal molecules.

The VHR value is measured as follows: The LC mixture is introduced intoVA-VHR test cells which comprise an unrubbed VA-polyimide alignmentlayer. The LC-layer thickness d is approx. 3 μm, unless statedotherwise. The VHR value is determined before and after light exposureat 1 V, 60 Hz, 64 μs pulse (measuring instrument: Autronic-MelchersVHRM-105).

Comparison Example 1

The nematic LC host mixture C1 is formulated as follows.

CC-3-V 24.50% cl.p. 85.9° C. CC-3-V1 12.00% Δn 0.0933 CCP-V-1 13.50% Δε−3.3 CPY-3-O2 1.00% ε_(∥) 3.4 CCY-5-O2 3.00% γ₁ 101 mPa s CLY-3-O2 9.00%K₁ 15.6 CLY-4-O2 5.50% K₃ 18.0 CLY-5-O2 5.50% K₃/K₁ 1.15 CY-3-O2 12.00%V₀ 2.46 V CY-3-O4 4.00% CY-5-O2 4.00% B(S)-2O-O4 4.00% B(S)-2O-O5 2.00%

Example 1

The LC mixture N1 is formulated by mixing 99.5% of the LC host mixtureC1 and 0.5% of the compound LB(S)-3-OT of formula LB2-2.

Example 2

The LC mixture N2 is formulated by mixing 99.0% of the LC host mixtureC1 and 1.0% of the compound LB(S)-3-OT of formula LB2-2.

Example 3

The LC mixture N3 is formulated by mixing 97.0% of the LC host mixtureC1 and 3.0% of the compound LB(S)-3-OT of formula LB2-2.

Example 4

The LC mixture N4 is formulated by mixing 99.5% of the LC host mixtureC1 and 0.5% of the compound LB-3-T of formula LB1-1.

Example 5

The LC mixture N5 is formulated by mixing 99.0% of the LC host mixtureC1 and 1.0% of the compound LB-3-T of formula LB1-1.

Example 6

The LC mixture N6 is formulated by mixing 97.0% of the LC host mixtureC1 and 3.0% of the compound LB-3-T of formula LB1-1.

VHR Values

The VHR values of mixtures C1 and N1 to N3 are measured at 60° C., 3 Hzin UB-FFS VHR test cells before and after light exposure for varyingtime using a LED lamp.

The results are shown in Table 1.

TABLE 1 VHR values C1 N1 N2 N3 VHR at 60° C. (%) VHR/% Initial 95.3 95.094.9 94.6 After 24 h Light stress 90.8 90.7 90.4 89.4 After 72 h Lightstress 84.9 85.2 83.8 82.1 After 168 h Light stress 74.2 74.5 73.0 68.9After 240 h Light stress 66.9 68.1 66.4 60.9

From Table 1 it can be seen that the mixtures N1 to N3 according to thepresent invention show VHR values which are comparable to those ofreference mixture C1.

White Flicker

The white flicker values of mixtures C1 and N1 to N3 are measured at 25°C., 10 Hz with V100 voltage loading in UB-FFS test cells.

The results are shown in Table 2.

TABLE 2 White flicker at V 100, 10 Hz, 25° C. C1 N1 N2 N3 White flicker1.9 1.3 1.4 1.3

From Table 2 it can be seen that the mixtures N1 to N3 according to thepresent invention show significantly reduced white flicker compared toreference mixture C1.

Easy Axis Shift by AC Loading

The easy axis shift ΔΦ of mixtures C1 and N1 to N3 are measured at 0voltage, room temperature for 90 min after stress which 10 Vrms for 2hrs at 30 Hz in UB-FFS test cell.

The results are shown in Table 3.

TABLE 3 ΔΦ by AC loading ΔΦ C1 N1 N2 N3 0 min 0.11 0.09 0.10 0.09 30 min0.03 0.02 0.02 0.03 60 min 0.02 0.01 0.01 0.03 90 min 0.01 0.01 0.010.02

From Table 3 it can be seen that the mixtures N1 to N3 according to thepresent invention show lower easy axis shift ΔΦ compared to referencemixture C1.

The preceding examples can be repeated with similar success bysubstituting the generically or specifically described reactants and/oroperating conditions of this invention for those used in the precedingexamples.

From the foregoing description, one skilled in the art can easilyascertain the essential characteristics of this invention and, withoutdeparting from the spirit and scope thereof, can make various changesand modifications of the invention to adapt it to various usages andconditions.

1. A liquid crystal (LC) medium having negative dielectric anisotropyand comprising one or more compounds of formula LB

in which the individual radicals, on each occurrence identically ordifferently, and each, independently of one another, have the followingmeaning: R¹ alkyl, alkoxy, oxaalkyl or alkoxyalkyl having 1 to 9 C atomsor alkenyl or alkenyloxy having 2 to 9 C atoms, all of which areoptionally fluorinated, L¹, L² F or Cl, X¹ fluorinated alkyl or alkoxywith 1, 2 or 3 C atoms, Y¹ O or S. R¹, R² alkyl, alkoxy, oxaalkyl oralkoxyalkyl having 1 to 9 C atoms or alkenyl or alkenyloxy having 2 to 9C atoms, all of which are optionally fluorinated, L¹, L² F or Cl.
 2. TheLC medium according to claim 1, wherein the compounds of formula LB are:


3. The LC medium according to claim 1, wherein the compounds of formulaLB are


4. The LC medium according to claim 1, additionally comprising one ormore compounds of formulae AN or AY

in which individual radicals, on each occurrence identically ordifferently, and each, independently of one another, have the followingmeaning:

R^(A1) alkenyl having 2 to 9 C atoms or, if at least one of the rings X,Y and Z denotes cyclohexenyl, also one of the meanings of R^(A2), R^(A2)alkyl having 1 to 12 C atoms, in which, in addition, one or twonon-adjacent CH₂ groups may be replaced by —O—, —CH═CH—, —CO—, —OCO— or—COO— in such a way that O atoms are not linked directly to one another,Z^(x) —CH₂CH₂—, —CH═CH—, —CF₂O—, —OCF₂—, —CH₂O—, —OCH₂—, —CO—O—, —O—CO—,—C₂F₄—, —CF═CF—, —CH═CH—CH₂O—, or a single bond, L¹⁻⁴ H, F, Cl, OCF₃,CF₃, CH₃, CH₂F or CHF₂H, x 1 or 2, z 0 or
 1. 5. The LC medium accordingto claim 1, additionally comprising one or more compounds of formulae CYor PY:

in which individual radicals have the following meanings: a denotes 1 or2, b denotes 0 or 1,

R¹ and R² each, independently of one another, denote alkyl having 1 to12 C atoms, where, in addition, one or two non-adjacent CH₂ groups maybe replaced by —O—, —CH═CH—, —CO—, —O—CO— or —CO—O— in such a way that Oatoms are not linked directly to one another, Z^(x) denotes —CH═CH—,—CH₂O—, —OCH₂—, —CF₂O—, —OCF₂—, —O—, —CH₂—, —CH₂CH₂— or a single bond,L¹⁻⁴ each, independently of one another, denote F, Cl, OCF₃, CF₃, CH₃,CH₂F, CHF₂.
 6. The LC medium according to claim 1, additionallycomprising one or more compounds of formulae ZK or DK:

in which individual radicals on each occurrence, identically ordifferently, have the following meanings:

and R³ and R⁴ each, independently of one another, denote alkyl having 1to 12 C atoms, in which, in addition, one or two non-adjacent CH₂ groupsmay be replaced by —O—, —CH═CH—, —CO—, —O—CO— or —CO—O— in such a waythat O atoms are not linked directly to one another, Z^(y) denotes—CH₂CH₂—, —CH═CH—, —CF₂O—, —OCF₂—, —CH₂O—, —OCH₂—, —COO—, —OCO—, —C₂F₄—,—CF═CF— or a single bond, R⁵ and R⁶ each, independently of one another,denote alkyl having 1 to 12 C atoms, where, in addition, one or twonon-adjacent CH₂ groups may be replaced by —O—, —CH═CH—, —CO—, —OCO— or—COO— in such a way that O atoms are not linked directly to one another,preferably alkyl or alkoxy having 1 to 6 C atoms, e denotes 1 or
 2. 7.The LC medium according to claim 1, additionally comprising one or morecompounds of formulae:

in which R and R′ each, independently of one another, denote astraight-chain alkyl or alkoxy radical having 1-7 C atoms.
 8. An LCdisplay comprising an LC medium as defined in claim
 1. 9. The LC displayof claim 8, which is a VA, SA-VA, IPS, PS-IPS, FFS, PS-FFS, UB-FFS orPS-UB-FFS display.
 10. A process of preparing an LC medium according toclaim 1, comprising mixing one or more compounds of formula LB with oneor more compounds selected from formulae AN, AY, CY and PY andoptionally with further LC compounds and/or additives,

in which individual radicals, on each occurrence identically ordifferently, and each, independently of one another, have the followingmeaning:

R^(A1) alkenyl having 2 to 9 C atoms or, if at least one of the rings X,Y and Z denotes cyclohexenyl, also one of the meanings of R^(A2), R^(A2)alkyl having 1 to 12 C atoms, in which, in addition, one or twonon-adjacent CH₂ groups may be replaced by —O—, —CH═CH—, —CO—, —OCO— or—COO— in such a way that O atoms are not linked directly to one another,Z^(x) —CH₂CH₂—, —CH═CH—, —CF₂O—, —OCF₂—, —CH₂O—, —OCH₂—, —CO—O—, —O—CO—,—C₂F₄—, —CF═CF—, —CH═CH—CH₂O—, or a single bond, L¹⁻⁴ H, F, Cl, OCF₃,CF₃, CH₃, CH₂F or CHF₂H, x 1 or 2, z 0 or 1,

in which individual radicals have the following meanings: a denotes 1 or2, b denotes 0 or 1,

R¹ and R² each, independently of one another, denote alkyl having 1 to12 C atoms, where, in addition, one or two non-adjacent CH₂ groups maybe replaced by —O—, —CH═CH—, —CO—, —O—CO— or —CO—O— in such a way that Oatoms are not linked directly to one another, Z^(x) denotes —CH═CH—,—CH₂O—, —OCH₂—, —CF₂O—, —OCF₂—, —O—, —CH₂—, —CH₂CH₂— or a single bond,L¹⁻⁴ each, independently of one another, denote F, Cl, OCF₃, CF₃, CH₃,CH₂F, CHF₂.